Much of the effort to develop a high temperature superconducting (HTS) wire or tape has focused on coated conductors based on the epitaxial growth of high temperature superconducting (HTS) films on tapes that possess a biaxially-textured surface. Superconducting films with critical current densities in excess of 1 MA/cm2 at 77 K and self-field have been achieved for epitaxial YBa2Cu3O7 films on biaxially-textured tapes produced either by ion-beam assisted deposition (IBAD) or thermomechanically-textured metals.
In previous work involving IBAD, the synthesis of the biaxially-textured buffer layer suitable for HTS films capable of carrying high critical current densities has employed the ion-assist process to produce both the in-plane and out-of-plane texture. In order to realize an HTS film possessing a high critical current on a biaxially textured substrate, the buffer layer architecture should satisfy rigorous requirements. The grains within the topmost buffer layer construct desirably provide a common in-plane and out-of-plane crystallographic texture with a mosaic spread of generally less than 20 degrees, with lower mosaic spreads such as less than 10 degrees providing better superconducting articles.
The top layer should generally be chemically compatible with the superconductor so as to not react during superconductor deposition and be mechanically robust to prevent microcrack formation at the HTS/buffer layer interface. To date, biaxially textured buffer layers that have met these objectives generally rely on the use of the ion-assist (IBAD) process in determining the in-plane and out-of-plane texture. For example, biaxially textured yttria-stabilized zirconia (YSZ) buffer layer can be formed by IBAD with the (100) in-plane and (001) out-of-plane texture by directing an Ar+ beam flux oriented 55 degrees from the surface normal, which corresponds to the [111] direction for a (001)-oriented cubic material.
While the above-described IBAD process has provided the desired biaxial texture requiring a relatively high thickness (>1 μm), such as by use of a YSZ film deposited in the presence of the Ar+ beam, the process is relatively slow and as a result expensive. The speed and price of such process is a significant issue in the large-scale production of superconducting tapes since it would affect the ability to produce a low-cost HTS tape. A second approach involves the IBAD deposition of MgO requiring a sub-10 nm control of the nucleation process, typically employing an in-situ monitoring technique, such as reflection high energy electron diffraction, for controlling the crystallographic texture. This approach is difficult to employ for large-scale production. Also, the quality of MgO films deposited by IBAD has been found to be extremely sensitive to minor variations in the processes and structures used for this material.
Accordingly, there is a need in the art for improved superconductor components, including coated HTS conductors, processes for forming same, and articles incorporating same. In particular, there is a need for commercially viable HTS conductors having characteristics enhancing large-scale production, and processes for forming the same.
Accordingly, there is also a need in the art for an alternative technique that would require less thickness than that required for IBAD of YSZ, but would be more robust and less sensitive than the IBAD process for MgO.